The human eye is a remarkably effective organ adaptable to a wide range of ambient light levels which can be functionally enhanced or improved by a host of optical instruments. For instance, visual function can be extended beyond the visible spectrum into the infrared portion of the spectrum by using night vision goggles and forward looking infrared devices (e.g., FLIDs) which are applicable to industrial applications, but particularly suited for military applications.
Night vision goggles (NVGs) are a helmet mounted binocular image intensifier. Head mounted night vision goggles are known and some of which are described in U.S. Pat. Nos. 5,361,162 and 5,617,257 both of which are herein incorporated by reference. The NVG provides the user with a 30 to 40 degree intensified field of view with an enhanced acuity at low ambient light levels (quarter moon down through starlight).
Once the human eye of the user becomes adapted to a dimly lit background, the NVG provides the user with vision therein. However, the vision in this dimly lit background may be disturbed or destroyed, or more importantly, the NVG and/or human eye may be damaged by the occurrence of sudden bright visual light, such as that created by a laser.
The human eye may be protected and even not disturbed by the bright light created by a laser by using a laser interference filter having the form of an optical lens and incorporated into goggles that are commonly used around laser equipment, some of which may create intense heat sufficient to cut metal. It is desired to incorporate the optical laser interference filter into night vision goggles so as to protect the NVG and/or human eye from being harmed or even disturbed by the bright visual light created by a laser source.
Night vision goggles (NVG) commonly comprise an objective lens that is positioned so as to face the object being viewed by the user and has a bezel on its rim defined by the outer diameter of the objective lens. Similarly, goggles used around laser equipment commonly incorporate an optical laser interference filter that is positioned to face the object being viewed by the user and has a bezel on its rim defined by the outer diameter of the optical laser interference filter.
The night vision goggles originally had tubes that were fitted with the NVG Head Up Display (HUD), which is a device that presents critical flight, engine and armament information in the form of symbology, to the pilot. The NVG and the HUD are completely separate pieces of equipment; i.e., the NVGs can be considered aircrew equipment, while the HUD is aircraft equipment.
Recently, the laser interference filter (LIF) was incorporated onto the NVG tubes to protect the tubes from laser induced damage. The LIF is installed by gluing a bezel onto the outer diameter of the NVG tubes, thereby, increasing effectively the diameter to about 17/16 inches. With this modification, the NVG HUD cannot be fastened onto the NVGs as before. It is desired that means be provided for fitting the NVG HUD onto the LIF bezel.